Personal Digital Assistant (PDA) is a generic name for a handheld personal computing device having a volume in the range of 200 to 1200 cubic centimeters. PDAs having as much computing power as some desktop personal computers are newly available from many manufacturers. Competition among of manufacturers of PDAs for market share in this new market has driven prices low enough to be attractive for applications where location and computing power have been needed but have not been affordable previously.
The new PDAs have a user interface including a liquid crystal display, a user entry mechanism, memory for application programs, and an interface for external electronic equipment. Existing PDAs include one or more Personal Computer Memory Card International Association (PCMCIA) interface cards that insert into slots in the PDA for the application program memory. Some PDAs include a speaker. The user entry typically includes an array of keys, a touch screen on the display, or both. The PCMCIA memory cartridge stores pre-coded software data and/or program instructions for an application and plugs into the PCMCIA slot in the PDA to give the appearance of a single, packaged unit. The processing system in the PDA includes a microprocessor, memory, pre-coded software in the memory, and associated logic hardware to operate the elements in the PDA, the memory cartridge, and the serial interface.
A PDA has an appearance that is similar to existing handheld, electronic video game devices. A limitation of handheld game devices is that the microprocessors used in the processing systems are not powerful enough to run application programs written in general purpose, high level languages such as C. A software application intended for a handheld game must be written in a language intended for the specific microprocessor used in the game processing system. An existing software application intended for another microprocessor must be re-written in order to use the applications with a handheld game device. A second limitation of handheld game devices is that the processing systems cannot run standard operating systems such as DOS, Windows, Macintosh, or Geoworks. Software applications that run in standard operating systems must also be re-written to be used in a handheld game device.
Printed maps are available for viewing almost all features that have geographical locations. A limitation of printed maps is that a user must manually sort through the entire map in order to find the geographical features that are proximate to his location. Each time a user travels to a new location, he must repeat this sort. Some maps include attributes of map features, such as an aviation map that includes airport signal frequencies or runway lengths. Typically, a separate page or a separate printed map for each set of attributes is required and must be manually sorted by the user.
Electronic maps have recently become available to replace paper maps for some applications. A map database is stored in a memory storage device as a bit map or raster, or as vectors that point to a map character. In a raster map database, data stored sequentially in memory represents the intensity and/or color of sequential pixels of a map. A map character is an alphanumeric or other determined shape. In a vector map database, data stored in memory represents the coordinates, intensity, character, and/or color of pixels of a map. The map database may also store characters that are superimposed on the display of the map, where characters are in ASCII or a similar format. Multiple colors or gray scales require additional data stored in memory for each pixel. Raster maps are easier to develop and less likely to have errors, but vector maps can be compressed into less memory and are more easily sorted for features and attributes. A combination of raster, vector, and character mapping may be used. Where the map database is too large for the memory storage device, the database may be divided into a plurality of modules, sometimes overlapping. An electronic display such as a liquid crystal display (LCD), electroluminescent (EL), cathode ray tube (CRT), or other similar electronic technology is used to display the map to the user. Keys or other user input devices are used to zoom in and out and to pan the map.
A limitation of an electronic map is that the electronic map features or attributes must be manually sorted by zooming and panning unless location is known and electrically communicated to the map application. Raubenhiemer et al. in U.S. Pat. No. 5,059,970 disclose an invention for the manual entry of location to an electronic map, where the invention electronically sorts the map so that a portion of the map proximate to the location is displayed. Provision is made for manual entry of speed, heading, and drift. A limitation of the Raubenhiemer et al. invention is that the location is susceptible to error in the manual entry and to accumulation of additional error as the user travels from his initial entered location if the entered speed, heading, and drift are not actual speed, heading, and drift.
Many electronic location determination systems are available or have been proposed to provide electronic location information to a user equipped with a location determination receiver. Ground-based location determination systems, such as Loran, Omega, TACAN, Decca, U.S. Airforce Joint Tactical Information Distribution System (JTIDS Relnav), or U.S. Army Position Location and Reporting System (PLRS), use the intersection of hyperbolic surfaces to provide location information. A representative ground system is LORAN-C discussed in LORAN-C User Handbook, Department of Transportation, U.S. Coast Guard, Commandant Instruction M16562.3, May 1990, which is incorporated by reference herein. LORAN-C provides a typical location accuracy of approximately 400 meters. A limitation of a LORAN-C location determination system is that not all locations in the northern hemisphere, and no locations in the southern hemisphere, are covered by LORAN-C. A second limitation of LORAN-C is that the typical accuracy of approximately 400 meters is insufficient for many applications. A third limitation of LORAN-C is that weather, local electronic signal interference, poor crossing angles, closely spaced time difference hyperbolas, and skywaves frequently cause the accuracy to be significantly worse than 400 meters.
Other ground-based location determination devices use systems that were developed primarily for communications, such as cellular telephone, FM broadcast, and AM broadcast. Some cellular telephone systems provide estimates of location, using comparison of signal strengths from three or more sources. FM broadcast systems having subcarrier signals can provide estimates of location by measuring the phases of the subcarrier signals. Kelley et al. in U.S. Pat. No. 5,173,710 disclose a system that allows determination of a location of a vehicle. FM subcarrier signals are received from three FM radio stations with known locations but unknown relative phases by signal processors at the vehicle and at a fixed station having a known location. The fixed station processor determines the relative phase of the signals transmitted by the three FM radio stations and transmits the relative phase information to the vehicle. The vehicle processor determines its location from the FM subcarrier signal phases and from the relative phase information it receives. A limitation of cellular systems and FM subcarrier systems for location determination is that they are limited to small regions, with diameters of the order of 20-50 km.
Satellite-based location determination systems such as Global Positioning System, GPS, and the Global Orbiting Navigational System, GLONASS, use the intersection of spherical surface areas to provide location information with a typical accuracy of 100 meters, anywhere on or near the surface of the earth. The satellite-based location determination systems include satellites having signal transmitters to broadcast location information and control stations on earth to track and control the satellites. Location determination receivers process the signals transmitted from the satellites and provide location information to the user.
The Global Positioning System (GPS) is part of a satellite navigation system developed by the United States Defense Department under its NAVSTAR satellite program. A fully operational GPS includes up to 24 satellites approximately uniformly dispersed around six circular orbits with four satellites each, the orbits being inclined at an angle of 55.degree. relative to the equator and being separated from each other by multiples of 60.degree. longitude. The orbits have radii of 26,560 kilometers and are approximately circular. The orbits are non-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital time intervals, so that the satellites move with time relative to the Earth below. Theoretically, four or more GPS satellites will have line of sight to most points on the Earth's surface, and line of sight access to three or more such satellites can be used to determine an observer's position anywhere on the Earth's surface, 24 hours per day. Each satellite carries a cesium or rubidium atomic clock to provide timing information for the signals transmitted by the satellites. Internal clock correction is provided for each satellite clock.
A second configuration for global positioning is the Global Orbiting Navigation Satellite System (GLONASS), placed in orbit by the former Soviet Union and now maintained by the Russian Republic. GLONASS also uses 24 satellites, distributed approximately uniformly in three orbital planes of eight satellites each. Each orbital plane has a nominal inclination of 64.8.degree. relative to the equator, and the three orbital planes are separated from each other by multiples of 120.degree. longitude. The GLONASS circular orbits have smaller radii, about 25,510 kilometers, and a satellite period of revolution of 8/17 of a sidereal day (11.26 hours). A GLONASS satellite and a GPS satellite will thus complete 17 and 16 revolutions, respectively, around the Earth every 8 sidereal days. The signal frequencies of both GPS and GLONASS are in L-band (1 to 2 GHz).
Because the signals from the satellites pass through the tropospheric for only a short distance, the accuracy of satellite location determination systems such as GPS or GLONASS is largely unaffected by weather or local anomalies. A limitation of GLONASS is that it is not clear that the Russian Republic has the resources to complete and to maintain the system for full world wide 24 hour coverage. The inherent accuracy of the GPS position measured by a commercial GPS receiver is approximately 20 meters. However, the United States Government currently degrades the accuracy of GPS positions for commercial users with Selective Availability, SA. With SA the GPS position accuracy of a commercial GPS receiver is approximately 100 meters.
Differential Global Positioning System, DGPS, is a service for enhancing the accuracy of the GPS position. The DGPS comprises the Global Positioning System together with a GPS reference station receiver situated at a known position. DGPS error correction information is derived by taking the difference between the measurements made by the GPS reference station and the expected measurement at the known position of the reference station. DGPS error correction information can be in the form of GPS satellite pseudorange offsets or GPS position offsets. If GPS position offsets are used, the GPS satellites used in the calculation of the GPS position must be included as part of the DGPS error correction information. A processor in a "differential-ready" GPS receiver applies the DGPS error correction information to enhance the GPS position to an accuracy in the range of 10 meters to a less than one meter.
Two types of DGPS exist, postprocessed and realtime. In postprocessed systems the DGPS error correction information and a user's GPS position information are processed after the user has completed his application. In realtime systems the DGPS error correction information is transmitted to the GPS user in a DGPS radio wave signal and processed by a differential-ready GPS receiver as the application progresses. Realtime processing is desirable for many applications because the enhanced accuracy of DGPS is available to the GPS user while he is working in the field. Realtime broadcast of DGPS error correction information is available from many sources, both public and private, including Coast Guard RDF beacon and commercially operated FM broadcast subcarrier. A DGPS radio wave receiver is required to receive the DGPS radio wave signal containing the DGPS error correction information and pass the DGPS error corrections to the differential-ready GPS receiver.
Many applications of GPS including mineral surveying, mapping, adding attributes or features to maps, finding sites on a map, vehicle navigation, airplane navigation, marine navigation, field asset management, geographical information systems, and others require the enhanced accuracy that is available with DGPS. For instance, a 20 to 100 meter error could lead to unintentional trespassing, make the return to an underground asset difficult, or put a user on the wrong block while walking or driving in a city. These applications require a computer to store and process data, retain databases, perform calculations, display information to a user, and take input from a user entry. For instance the user may need to store a map database, display a map, add attributes to features on the map, and store these attributes for geographical information. Or he may need to store and display locations or calculate range and bearing to another location.
GPS is used by many professionals engaged in navigation and surveying fields such as marine navigation, aircraft piloting, seismology, boundary surveying, and other applications where accurate location is required or where the cost of GPS is small compared to the cost of a mistake in determining location. Some professionals engaged in mobile fields such as utilities, insurance, ranching, prospecting, ambulance driving, trucking, delivery, police, fire, real estate, forestry, and other mobile applications use GPS to save time in their work. GPS is also used for personal travel such as hiking, biking, horseback riding, yachting, fishing, driving in personal cars, and other travel activities. However, most mobile professional and personal users of GPS find that location coordinates as provided by GPS are of limited use unless the proximate map features and/or attributes are sorted and displayed in the same coordinate system.
In many aviation, marine, vehicle, and pedestrian navigation applications, the navigator uses personal navigation equipment that he carries with him when he changes airplanes, boats, or motor vehicle to save the cost of having multiple sets of navigation equipment or to prevent theft of the equipment. The navigation equipment for these applications needs to be easily installed and removed. Most existing GPS receivers are designed to be hard mounted onto a platform so that the equipment is not easily removed. The Federal Aviation Agency (FAA) is rightfully concerned that unqualified navigation equipment carried in aircraft may interfere with the proper operation of the aircraft. For this reason the FAA has a time consuming and expensive testing requirement to qualify navigation equipment. However, the FAA has traditionally allowed extra navigation equipment to be carried aboard so long as the equipment is not hard mounted to the aircraft or powered from the aircraft power supply. Existing handheld GPS receivers operate from internal batteries and are easy to install and remove, but have limited or no computing power, databases, or map display and cannot use applications programmed in standard operating systems.
Many systems using handheld computers, having computing power for maps and for standard operating systems, have been coupled to GPS Smart Antennas. Wireless, infrared, serial, parallel, and PCMCIA interfaces have been used to interconnect the handheld computer and the GPS Smart Antenna. Differential-ready GPS Smart Antennas having an input to receive signals representative of DGPS error corrections are commercially available. A GPS receiver built onto a type II PCMCIA card is commercially available. A differential-ready GPS Smart Antenna with an integral DGPS receiver has been reduced to practice. A DGPS receiver built onto a PCMCIA card and a system including a GPS receiver on a PCMCIA card, a DGPS receiver on a PCMCIA card, and a handheld computer has been reduced to practice. None of the systems having a handheld computer and a GPS location determination device include a separate memory storage device that is used exclusively for an application program. None of these systems explicitly discuss a memory storage device that may be conveniently reprogrammed with a new application. A limitation of these systems is that a user cannot easily change his application program without purchasing duplicate GPS hardware.
What is needed is an handheld apparatus having a GPS antenna and receiver to provide location information, capable of using standard operating systems such as DOS, Windows, Macintosh, or Geoworks to run existing applications, and capable of running programs written in high level languages such as C to provide a mobile professional, a personal traveler, or a navigator with a display of his location and relative locations and the attributes of map features proximate to him. The apparatus needs to operate from an internal source of power, be convenient to install and remove, and have a replaceable memory storage device used exclusively to store applications programs or a memory storage device that may be conveniently reprogrammed. Location accuracy within 10 meters or less needs to be available to the user.